Glucose-6-phosphate dehydrogenase of the corpus luteum of the ovary is a specific receptor for luteinizing hormones (LH and HCG). Activation of the enzymes by these trophic hormones stimulates the formation of ribose phosphate by the pentose phosphate pathway and increases the production of phosphoribosylpyrophosphate (PP-ribose-P). PP-ribose-P is rate-limiting to the biosynthesis of purine and pyrimidine nucleotides and to RNA synthesis in in vitro preparations prepared from corpora lutea of the pig, cow, and human ovary. LH or HCG at a concentration of 1 nM stimulates ribonucleotide biosynthesis as much as 3-fold in ten minutes. The beta subunits of these hormones at the same concentration block the stimulatory effect of the intact hormone. These interactions of the beta subunit and LH or HCG with the receptor site are being used as a model for the design of contraceptive agents.